The present invention relates to an electronic circuit device in which electric power is transmitted between a primary side and a secondary side of a transformer.
As a conventional electronic circuit device, for instance, Japanese Patent Publication Number 2012-134291 discloses a switching power supply device explained below. The switching power supply device has a transformer as one of its parts. The transformer is configured with a core, a primary winding and a secondary winding. Further, the switching power supply device transmits electric power by magnetically connecting between the primary winding and the secondary winding via the core while realizing electrical insulation.
In Japanese Patent Publication Number 2012-134291, the transformer has a sheet transformer configuration and a switching element (a switch) that is provided at a primary side of the transformer. The transformer and the switching element are configured as different parts. Further, the transformer and the switching element are separately mounted on a board. That is, because the transformer and the switching element are spaced apart from each other at the mounting points of the transformer and the switching element, an area of the board naturally becomes large. Thus, because the device increases in size, a parasitic inductance of the circuit increases.
As countermeasures for these problems explained above, a non-patent literature, Daocheng Huang, Shu Jin, Fred C. Lee, “Matrix transformer for LLC resonant converters” (Applied Power Electronics Conference and Exposition (APEC)), March 2013, Twenty-Eight Annual IEEE, Pages 2078-2083; Digital Object Identifier 10.1109/APEC.2013.6520582, discloses LLC resonant converters. The disclosed LLC resonant converter has a synchronous rectification switching element and a smoothing capacitor as a secondary side circuit of a transformer. A distance between the transformer and the secondary side circuit is shortened by mounting the synchronous rectification switching element and the smoothing capacitor explained above in a middle of a secondary winding of the transformer.
The LLC resonant converter that is disclosed in the non-patent literature is as follows: the secondary winding is formed in a pattern at an outer layer of a stacked board and the secondary side element such as the synchronous rectification switching element and the smoothing capacitor are directly mounted in the middle of the secondary winding on a surface of the board. However, because a primary winding of the transformer is formed in a pattern in an internal layer of the board, a primary side element cannot be mounted in a middle of the primary winding. As a result, a miniaturization of an entire device cannot be realized.